一、class_ro_t 的 flags 標識
// Values for class_ro_t->flags
// These are emitted by the compiler and are part of the ABI.
// Note: See CGObjCNonFragileABIMac::BuildClassRoTInitializer in clang
// class is a metaclass
#define RO_META (1<<0)
// class is a root class
#define RO_ROOT (1<<1)
// class has .cxx_construct/destruct implementations
#define RO_HAS_CXX_STRUCTORS (1<<2)
// class has +load implementation
// #define RO_HAS_LOAD_METHOD (1<<3)
// class has visibility=hidden set
#define RO_HIDDEN (1<<4)
// class has attribute(objc_exception): OBJC_EHTYPE_$_ThisClass is non-weak
#define RO_EXCEPTION (1<<5)
// class has ro field for Swift metadata initializer callback
#define RO_HAS_SWIFT_INITIALIZER (1<<6)
// class compiled with ARC
#define RO_IS_ARC (1<<7)
// class has .cxx_destruct but no .cxx_construct (with RO_HAS_CXX_STRUCTORS)
#define RO_HAS_CXX_DTOR_ONLY (1<<8)
// class is not ARC but has ARC-style weak ivar layout
#define RO_HAS_WEAK_WITHOUT_ARC (1<<9)
// class does not allow associated objects on instances
#define RO_FORBIDS_ASSOCIATED_OBJECTS (1<<10)
// class is in an unloadable bundle - must never be set by compiler
#define RO_FROM_BUNDLE (1<<29)
// class is unrealized future class - must never be set by compiler
#define RO_FUTURE (1<<30)
// class is realized - must never be set by compiler
#define RO_REALIZED (1<<31)
二、class_rw_t 的 flags 標識
// Values for class_rw_t->flags
// These are not emitted by the compiler and are never used in class_ro_t.
// Their presence should be considered in future ABI versions.
// class_t->data is class_rw_t, not class_ro_t
#define RW_REALIZED (1<<31)
// class is unresolved future class
#define RW_FUTURE (1<<30)
// class is initialized
#define RW_INITIALIZED (1<<29)
// class is initializing
#define RW_INITIALIZING (1<<28)
// class_rw_t->ro is heap copy of class_ro_t
#define RW_COPIED_RO (1<<27)
// class allocated but not yet registered
#define RW_CONSTRUCTING (1<<26)
// class allocated and registered
#define RW_CONSTRUCTED (1<<25)
// available for use; was RW_FINALIZE_ON_MAIN_THREAD
// #define RW_24 (1<<24)
// class +load has been called
#define RW_LOADED (1<<23)
#if !SUPPORT_NONPOINTER_ISA
// class instances may have associative references
#define RW_INSTANCES_HAVE_ASSOCIATED_OBJECTS (1<<22)
#endif
// class has instance-specific GC layout
#define RW_HAS_INSTANCE_SPECIFIC_LAYOUT (1 << 21)
// class does not allow associated objects on its instances
#define RW_FORBIDS_ASSOCIATED_OBJECTS (1<<20)
// class has started realizing but not yet completed it
#define RW_REALIZING (1<<19)
// class is a metaclass (copied from ro)
#define RW_META RO_META // (1<<0)
